sealed will yield a fairly flat response, and is the most accurate type of box. a sealed box also requires the most power to attain the same SPL as other box types.
a ported box is usually about +3dB more efficient at the frequency of the tuned port(s). These boxes require less power than sealed to reach the same SPL, but below their tuned frequency, they are very hard to control, and require great amounts of power to produce those below-port frequencies. Ported enclosures also add coloration to the sound, which detracts from their accuracy.
bandpass boxes are +3 to +12dB more efficient, making these the loudest of the boxes, but they lack severely in sound quality and will not hit very deeply since they, as the name implies, are limited to a notch frequency range.. usually between about 50-100Hz. loud, not deep, and they can accept a lot of power due to the damping factor of the enclosure designs. Bandpass boxes are ideal for SPL competitions, but not recommended for anything desiring musicality such as a daily driver car.
Surely some mistake in above? I always believed that below port tuning frequency the speaker becomes unloaded causing a masive jump in cone movement, hence the need for subsonic filtering, so if you start pumping masive amounts of power into an unloaded speaker this sounds like a recipe for disaster. Bandpass boxes don't have to be tuned to a narrow peak they can be designed to have a wider bandwidth, at the expense of db gains. They can also be tuned low if bass extension is what you need.For example a Rockford 12 can be tuned from 32-106hz or 25-68hz both without any db gains. So bandpass boxes can go deep and wide. If the bass response is purely for spl then isn't a ported box tuned to the resonant frequency of your car the best way to get masive db gains? Taking the Rockford 12 and assuming a vehicle resonance of 60hz, tuning a bandpass box to a 60hz center frequency gets you a 6db gain but in a big ported box tuned to 60hz you can get a 12db gain.
Then again maybe I've got the wrong end of the stick,it has been known.
In order to reproduce frequencies below the tuned port frequency, the power required to do so increases by about tenfold. Below the tuned frequency, there is also a loss of damping, which causes the lack of control of the sub, and consequently, over-excursion. That was essentially what I said. End result being that a sealed box will yiend a flat response down to about 9Hz thanks to cabin gain compensating for roll-off. A ported box isn't much good below it's tuned frequency since it rolls off rather steeply below that frequency anyway, and the ports shouldn't ever be tuned to a frequency below that of the Fs of the driver again to avoid the loss of driver damping. The ported box though, at it's tuned frequency, is about +3dB in SPL compared to a sealed box which means it's a cheap way to get more bass. That's the whole idea behind a ported box in the first place though. Ideally, you'd use a sealed box, or even transmissionline, and just pump more power into the equasion to make higher SPL. That's not a cost effective approach though.
"a Rockford 12 can be tuned from 32-106hz or 25-68hz both without any db gains." yes and again, it'll suffer from coloration. that wide of a response won't give much in the way of gain either, which means you're probably talking 4th order anyway. Another downfall of bandpass boxes are that they take about 1.5-2X the amount of space a sealed box would require.
Okay as for tuning a box to the Fs of the cabin, have you ever actually heard a box that was tuned to 60Hz? It sounds a lot like two cats f***ing. Yes ideally for SPL you'd go with a banspass box, 6th or 8th order, if you have the skills to build it, which honestly few of us do, without blowing teh cones right out of the drivers the first time you give it some juice, and you would, yes, tune the ports to the resonant frequency of the vehicle after severely damping the entire car top to bottom. I'll note though, that SPL isn't my main focus. I think SPL cars are a waste of time and money. I've always focused far more on sound quality, which I suppose is why I prefer companies like DynAudio, Sinfoni, Eclipse, Onyx, Audiocontrol, and Zapco along with Krell, Mark Levinson, and MartinLogan at home. I was never big into "mine is louder than yours" after 150dB, it's all noise.
Ah Ha so I was right. My thoughts on generating vast spl figures are not my idea of a system you'd want to listen to, but just a way of getting the biggest boost from your box.
Still not conviced bandpass is best for ultimate spl although for getting a small gain ok. I can see the benfits of 6th order boxes of having bigger gains over greater bandwidth, but is it really worth it anyway? I'm sure most people opt for the bandpass as it has an urban legend about it, not forgetting the box internals look trick under plexi. I'm sure most people would be quite happy with just a plain sealed if thats what their subs needed. Not even the most hardend bass head drives round with the volume on max all day. Will that couple of db gained from box design really make any difference except in bragging rights. One question when talking 8th order are you refering to electrically assisted 6th order or "series tuned" (not sure if that's correct term) where the two chambers of a 6th order box are join with a port? I'm personally quite happy with 500rms and a couple of twelves in ported boxes designed arround my subs. Here's a thought once on the move will anyone actually notice small differences between alternate loadings, what with all the usual car noise going on? Assuming a good design in the first place.
-Still not conviced bandpass is best for ultimate spl
it is because with teh right design like 6th or 8th order, you gain a lot of efficiency in addition to increases in power handling, at the cost of space and sound quality. If SPL is your only concern, a 6th order box is going to deliver that at a very narrow band, which if done right, will be the same as the res freq of the vehicle's cabin. The real trick is being able to do both the math, and the construction to make teh box work for you, then having a vehicle and electrical system that can cope. The thing about SPL competitions, is that the people who win are the ones who have teh most money to sink into the vehicle. Be that pocket money or sponsorship. Aside from the lack of SQ you get from a pure SPL car, that's my main gripe with SPL events.
- I'm sure most people opt for the bandpass as it has an urban legend about it, not forgetting the box internals look trick under plexi.
that, and you can buy rather crappy ones for dirt cheap at BestBuy. Those prefab 4th order boxes look nifty to people who aren't savvy about car audio so yeah they do have a stigma. That and you can slap a single 10" sub in a 4th order box, and get a lot of bass out of it with a fairly small amplifier which means no new alternator, and no breaking the bank for the highschool kids who want the car to thump. They usually don't figure the downfalls of things like coloration, harmonics, or frequency response of the box.
- I'm sure most people would be quite happy with just a plain sealed if thats what their subs needed.
Sure if they have the power to drive that sealed box to it's peak performance, but that's the big problem.. most people can't afford that sort of power, or they buy subs without looking at things like the EBP calculations to see what type of box will be ideal for the subs they buy. Bandpass and Vented boxes are just ways to get more bass with less money/power/space.
-'m personally quite happy with 500rms and a couple of twelves in ported boxes designed arround my subs.
I used two 12" subs in a vented box I designed with 160WRMS x 2 to drive them, and between that and the other amp for mids/highs, I was hitting 151dB with a perfect soundcurve, so yeah power isn't everything.
-will anyone actually notice small differences between alternate loadings?
probably not. an RTA might though, sitting in the lanes at competitions.
- when talking 8th order...
like this: http://www.geocities.com/f4ier/subsim8BP1.htm or, a sixth order enclosure where the front and rear enclosures of the sub are vented into a secondary enclosure, which is then ported to "open air" they are a b*tch to design, and they sound like crap in general, but they sure hit hard. problem is, like a 6th order, one wrong figure, or measurement, and the first tiem you give the box some power, you wind up over-excursing the driver, and tearing the cone right out of the sub.
I will note, my favorite box type is a transmission line. They just don't work out too well in ust any application. You need the right speaker, the right box, and the right environment.
oh, that link was just for the picture they had there of an 8th order box as an example. first image I found because I was too lazy to draw one for this thread. heh